When a building has sunk due to poor underlying soil conditions, or failure of the foundation due to other causes, it can often be saved by raising it back to its original level. For this purpose piles must usually be driven into the ground under or adjacent to the foundation to provide a solid underpinning upon which force can be exerted for raising the sunken parts of the building and upon which the building is supported after repairs are completed.
U.S. Pat. No. 2,982,103 to Revesz et al discloses such a method of raising a building, wherein brackets are fastened to the sunken foundation wall at spaced locations along it and a hydraulic jack is mounted on each bracket. The jack is employed to drive a pile down alongside the foundation until the pile offers a predetermined resistance to further driving, the value of that resistance being determined by the load that the pile will be required to support. As the pile is driven down, the jack reacts between the foundation wall and the pile, which is to say that the building supports the upward reaction to the downward driving force that the jack exerts. When the pile reaches the desired depth, the bracket is connected to an upper end portion of it, so that the pile can then directly support the building and the jack can be removed for reuse. The connection between the bracket and the pile comprises a load plate that rests on the top of the pile and screw threaded connections between the load plate and the bracket whereby the weight of the building can be taken up at the same time that it is relieved from the hydraulic jack.
With the apparatus disclosed by this reference the jack necessarily has a somewhat limited stroke and the bracket on which it is mounted must be fairly close to the ground. As a result, the pile must be made up of a series of short sections that are coupled to one another as the pile is being driven. The patent specifies that the pile can be made up of pipe sections, each approximately four feet long. Such short sections of pipe tend to be relatively expensive per unit of length, since they usually have to be cut from longer standard lengths, and the cost of this composite pile is further increased by the numerous couplers needed for it. Further and very significant cost is, of course, involved in the labor and time required for connecting the short pipe sections as they are being driven.
U.S. Pat. No. 3,852,970, to Cassidy, discloses a generally similar arrangement wherein, however, the connection between the hydraulic jack and the bracket on the foundation wall provides for stepwise vertical adjustment of the jack to each of a number of locations. For such adjustment a pair of upright pipes are secured to the bracket in parallel, laterally spaced relation to one another, each having pin receiving holes at intervals along its length. A reaction block to which the upper end of the jack cylinder is fixed is adjustably secured at any desired position along the pipes by pins extending through it and into a hole in each of the pipes. With this arrangement the relatively short stroke of the jack can be effectively lengthened to a certain extent by bodily up and down adjustment of the jack cylinder, but it is still necessary to work with pile sections substantially shorter than standard length pile pipes and to devote time and labor to coupling these pile sections as they are being driven.
Conventional impact pile drivers can, of course, drive piling sections in standard lengths of about 25 ft. However, an impact pile driver is not suitable for use in underpinning an existing sunken building because of the severe damage to the building structure that is likely to result from its impact shocks, transmitted to the building through the ground. For that matter, there are situations where an impact pile driver cannot or should not be used to drive piles for a new building, as where it must operate near a laboratory or the like having instruments that would be adversely affected or destroyed by the vibrations and shocks that it produces, or near a hospital where its noise cannot be tolerated.